Early hydrocarbon production system

ABSTRACT

A subsea hydrocarbon reserve is exploited by intially drilling a first well ( 4 ) from a floating drilling vessel ( 2 ). A tree ( 8 ) is then installed on the well ( 4 ) and a production riser ( 10 ) is established between the well and the vessel for transferring production fluid from the first well ( 4 ) to the vessel ( 2 ) from where an off-loading hose ( 12 ) conveys the production fluid to a tanker ( 18 ). Production fluid is then extracted from the first well ( 4 ) via the production riser ( 10 ) which is of sufficient flexibility and length to permit the drilling vessel ( 2 ) to move between appropriate locations to drill further wells ( 4′, 20 ).

[0001] The present invention relates to the development of a hydrocarbon extraction system and more particularly to the early stages of extraction of hydrocarbons from a subsea hydrocarbon deposit.

[0002] When a subsea hydrocarbon deposit is to be tapped, it is customary to drill a number of wells into the deposit, each of which is capped by a so-called “Christmas tree” or “tree”. Once a number of wells with associated trees have been established, a tree connecting manifold is installed on the sea bed which is linked to a pipeline for conveying production fluid from the wells to a floating or shore-based processing or storage facility for example. Since it commonly takes around a month to drill a well and install a tree on it, and a single drilling ship is used for this purpose, wells capped with a tree often remain unproductive for some months while the drilling ship drills other wells. Furthermore, the installation of a manifold: while drilling is in progress may present severe operational conflict problems. Such a manifold could be installed before or after drilling operations or while drilling a well some distance from, the location of the manifold.

[0003] An object of the invention is to overcome the above problem.

[0004] Thus, according to the invention, there is provided a method of exploiting a subsea hydrocarbon reserve comprising the steps of:

[0005] (i) drilling a first well from a floating drilling vessel;

[0006] (ii) establishing a production riser for transferring production fluid from the first well to the vessel or production fluid reception means closely associated with the vessel; and

[0007] (iii) extracting production fluid from the first well while drilling one or more further wells from the drilling vessel.

[0008] With such an arrangement, exploitation of the first well need not wait until all associated wells have been drilled. The consequent early production from the well can be used to generate revenue at an early stage, thus assisting cash flow.

[0009] Preferably, the production riser is sufficiently flexible to permit local excursions of the drilling vessel while it is drilling one of the further wells. More preferably, the production riser is of sufficient flexibility and length to permit the drilling vessel to move between appropriate locations for drilling plural further wells in order that output from two or more wells can be exploited while well drilling is still in progress.

[0010] Advantageously the method includes the step of establishing at least one further well and transferring production fluid from the first well and the at least one further well to the vessel or the production fluid reception means while drilling at least one additional well. Fluid may be conveyed from the further well;

[0011] (i) by an additional production riser to the vessel etc;

[0012] (ii) by ‘daisy chaining’ or interconnecting it with at least one other well so that the combined production flow from a number of wells is conveyed via common production riser; or

[0013] (iii) by installing a manifold to which the further well or wells is/are attached and the combined production flow is conveyed to the vessel etc. via the production riser.

[0014] The method may include processing the production fluid with processing means installed on the vessel. The method may also include the step of subsequently installing the processing means on the sea bed and carrying out subsea processing of production fluid from the wells by using the processing means.

[0015] The method may include conveying the production fluid to an off-loading buoy possibly by means of an off-loading hose extending from the drilling vessel to the buoy.

[0016] Production fluid reaching the buoy may be conveyed to a floating storage unit such as a tanker and may be stored for a period of time in the buoy while one such floating storage unit is removed for replacement by another. Alternatively, the buoy may be connected to a pipeline (e.g. a seabed pipeline) leading to a remote location such as a floating or shore-based storage or production facility.

[0017] The invention will now be described by way of example only with reference to the accompanying figures in which:—

[0018]FIG. 1 shows a first stage of the method according to the invention; and

[0019]FIG. 2 shows a second stage of the method according to the invention.

[0020]FIG. 1 shows a drilling vessel 2 drilling a first well 4 in the seabed 6 with a drill string 7. Once the well 4 has been completed, a first tree 8 is installed, on the well as shown in FIG. 2. Such trees are well known in the art and include valves for controlling the, flow of; production fluid from a hydrocarbon reservoir tapped by the well 4. A first flexible production riser 10 is installed between the first tree 8 and the vessel 2. The first flexible riser 10 may include buoyant means 11 for supporting at least a part of the weight of the flexible riser 10. Such flexible risers, including buoyancy means, are well known in the art.

[0021] An off-loading buoy 12 is moored in the vicinity of the first well 4 by means of mooring lines 14 connected to the sea bed 6. An off-loading hose 16 is installed for conveying production fluid etc. from the drilling vessel 2 to the off-loading buoy 12 and a floating storage unit, for example a tanker 18, is connected to the buoy 12 for receiving and storing production fluid etc. Production fluid may alternatively be routed from the buoy 12 to a sea bed pipeline for conveyance to a remote location.

[0022] The drilling vessel 2 then moves to an appropriate location as shown in FIG. 2 for drilling a second well 20. When this has been drilled, a second tree 22 (shown in broken lines) is installed thereon.

[0023] As indicated in FIG. 2 with broken lines, plural wells 4, 4′ may be connected to the drilling vessel 2 while the drilling vessel is drilling a further well 20. With such an arrangement, it is possible to exploit the production from two or more wells through the flexible production risers 10, 10′ while the further well 20 is being drilled. Alternatively, well 4′ and any subsequent well may be “daisy chained” to well 4 so that the combined production flow from both wells is conveyed to the vessel 2 by the flexible production riser 10. Alternatively, and not shown, a manifold may be installed to which wells 4′ and 4 and any subsequent wells are connected and the combined production flow routed to the vessel 2 either by the flexible riser 10, or by an additional flexible riser.

[0024] The drilling vessel 2 may have processing equipment 24 mounted thereon such as a processing module forming part of the modular system designed by Alpha Thames Limited of Essex, United Kingdom and named AlphaPRIME. The processing equipment may effect separation of different components of the production fluid from each other for separate conveyance to a remote location. The processing equipment 24 may be in the form of a module for installation as, part of a sea bed processing system such as that designed by Alpha Thames Limited.

[0025] Once drilling of all associated wells has been completed, production fluid from the wells will be routed to a remote location (before or after processing) via an alternative route, i.e. not via the flexible risers 10, 10′ and the drilling vessel 2. Production fluid may for example be routed to a sea bed processing unit which separates different constituents of the production fluid for conveyance through sea bed pipelines to a remote location.

[0026] The invention provides a method of exploiting output from one or more wells in a field prior to or while other wells are being drilled and other infrastructure fabricated or manufactured. This will: enable early exploitation of the, well to occur and assist cash flow by generating revenue at an earlier stage than has hitherto been possible. 

1. A method of exploiting a subsea hydrocarbon reserve, comprising the steps of drilling a first well (4) from a floating drilling vessel (2), establishing a production riser (10) for transferring production fluid from the first well (4) to the drilling vessel or production fluid reception means (18) closely associated with the vessel, and extracting production fluid from the first well (4) while drilling one or more further wells (20) from the drilling vessel (2), and characterised by the steps of: (i) processing the production fluid with processing means (24) installed on the drilling vessel (2); (ii) subsequently installing the processing means (24) on the seabed; and (iii) carrying out subsea processing of production fluid from the wells (4,4′,20) by using the processing means (24).
 2. A method as claimed in claim 1, wherein the processing means (24) is in the form of a module for installation as part of a seabed processing system.
 3. A method as claimed in claim 1, wherein the processing means (24) separates the production fluid into different components.
 4. A method as claimed in claim 1, wherein the production riser (10) is sufficiently flexible to permit local excursions of the drilling vessel (2) while it is drilling a said further well (20).
 5. A method as claimed in claim 1, wherein the production riser (10) is of sufficient flexibility and length to permit the drilling vessel (2) to move between appropriate locations for drilling plural further wells (20) in order that output from two or more wells (4,4′) can be exploited while well drilling is still in progress.
 6. A method as claimed in claim 5, including the step of establishing at least one further well (4′) and transferring production fluid from the first well (4) and the at least one further well (4′) to the drilling vessel (2) or the production fluid reception means (18) closely associated with the vessel while drilling at least one additional well (20).
 7. A method as claimed in claim 6, including conveying the production fluid from the drilling vessel (2) to an off-loading buoy (12) for onward conveyance.
 8. A method as claimed in claim 7, wherein said production fluid reception means comprises a floating storage unit (18), and the method includes storing production fluid for a period of time in the buoy (12) while the floating storage unit (18) is removed for replacement by another floating storage unit.
 9. A method as claimed in claim 1, including conveying the production fluid from the drilling vessel (2) to a pipeline leading to a remote location via an off-loading buoy (12).
 10. A method as claimed in claim 7, wherein production fluid is conveyed from the drilling vessel (2) to the buoy (12) by means of an off-loading hose (16) extending from the drilling vessel (2) to the buoy (12).
 11. A method as claimed in claim 10, wherein fluid is conveyed from a said further well (4′) by an additional production riser (10′) to the drilling vessel (2) or production fluid reception means (18).
 12. A method as claimed in claim 11, wherein fluid is conveyed from a said further well (4′) by interconnecting said further well (4′) with at least one other well (4) so that the combined production flow from a number of wells (4,4′) is conveyed via a common production riser (10).
 13. A method as claimed in claim 1, wherein fluid is conveyed from a said further well (4′) by installing a manifold to which the further well or wells is/are attached and the combined production flow is conveyed to the drilling vessel (2) or production fluid reception means (18) via the production riser (10). 